Properties of Triangles 1 Question 5

5. If the angles A,B and C of a triangle are in an arithmetic progression and if a,b and c denote the lengths of the sides opposite to A,B and C respectively, then the value of the expression acsin2C+casin2A is

(2010)

(a) 12

(b) 32

(c) 1

(d) 3

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Answer:

Correct Answer: 5. (d)

Solution:

  1. Since, A,B,C are in AP.

2B=A+C i.e. B=60

ac(2sinCcosC)+ca(2sinAcosA)

=2k(acosC+ccosA)

 using, asinA=bsinB=csinC=1k

=2k(b)

=2sinB [using b=acosC+ccosA ] =3



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